The dinoflagellate cyst assemblages from the northern shelf of the East China Sea were examined to assess their potential use as indicators of marine productivity in shelf environments. Coastal areas affected by fluvial freshwater input were dominated by protoperidinioid species, whereas open sea areas were dominated by gonyaulacoid species. The rarity of protoperidinioid cysts in the shelf sediment is primarily attributable to the deficit of silicate in the waters, associated with low supplies of suspended particulate matter from the adjacent continent. This would limit the growth of the protoperidinioid species, which feed on diatoms. In contrast, a constant supply of nitrogen generated by microbial nitrogen fixation appeared to support the production of gonyaulacoid species. This result suggests that gonyaulacoid dinoflagellate cysts are a potentially useful proxy indicator for low nutrient concentration levels, especially of silicate, in the shelf environment. were dominated by protoperidinioid species, whereas open sea areas were dominated by gonyaulacoid species. The rarity of protoperidinioid cysts in the shelf sediment is primarily attributable to the deficit of silicate in the waters, associated with low supplies of suspended particulate matter from the adjacent continent. This would limit the growth of the protoperidinioid species, which feed on diatoms. In contrast, a constant supply of nitrogen generated by microbial nitrogen fixation appeared to support the production of gonyaulacoid species. This result suggests that gonyaulacoid dinoflagellate cysts are a potentially useful proxy indicator for low nutrient concentration levels, especially of silicate, in the shelf environment.